The table below shows the distribution of the waiting times for some customers in a certain petrol station.

Waiting time (in mins)	No of customers
1.5 - 1.9	3
2.0 - 2.4	10
2.5 - 2.9	18
3.0 - 3.4	10
3.5 - 3.9	7
4.0 - 4.4	2

(a) Write down the class boundaries of the distribution.

(b) Construct a cumulative frequency curve for the data;

(c) Using your graph, estimate: (i) the interquartile range of the distribution ; (ii) the proportion of customers who could have waited for more than 3 minutes.